---
title: Backend Tools
icon: "lucide/Server"
description: Render your agent's tool calls with custom UI components.
---

import { Accordions, Accordion } from "fumadocs-ui/components/accordion";
import { IframeSwitcher } from "@/components/content"
import { Tabs, Tab } from "fumadocs-ui/components/tabs"
import DefaultToolRendering from "@/snippets/shared/guides/default-tool-rendering.mdx"
import RunAndConnect from "@/snippets/integrations/adk/run-and-connect.mdx"

<IframeSwitcher
  id="backend-tools-example"
  exampleUrl="https://feature-viewer.copilotkit.ai/adk-middleware/feature/backend_tool_rendering?sidebar=false&chatDefaultOpen=false"
  codeUrl="https://feature-viewer.copilotkit.ai/adk-middleware/feature/backend_tool_rendering?view=code&sidebar=false&codeLayout=tabs"
  exampleLabel="Demo"
  codeLabel="Code"
  height="700px"
/>

## What is this?

Tools are a way for the LLM to call predefined, typically, deterministic functions. CopilotKit allows you to render these tools in the UI
as a custom component, which we call **Generative UI**.

## When should I use this?

Rendering tools in the UI is useful when you want to provide the user with feedback about what your agent is doing, specifically
when your agent is calling tools. CopilotKit allows you to fully customize how these tools are rendered in the chat.

## Implementation

<Steps>
<Step>
### Run and connect your agent
<RunAndConnect components={props.components} />
</Step>
<Step>
### Give your agent a tool to call

<Tabs groupId="language_adk_agent" items={['Python']} default="Python" persist>
    <Tab value="Python">
        ```python title="agent.py"
        from fastapi import FastAPI
        from ag_ui_adk import ADKAgent, add_adk_fastapi_endpoint
        from google.adk.agents import LlmAgent


        def get_weather(location: str = "the entire world") -> str:
            """Retrieves the current weather report for a specified location.

            Args:
                location (str): The name of the location to get the weather for.

            Returns:
                str: The weather report for the specified location.
            """
            return f"The weather in {location} is sunny."


        agent = LlmAgent(
            model="gemini-2.5-flash",
            name="my_agent",
            instruction="You are a helpful weather assistant.",
            tools=[get_weather],
        )

        adk_agent = ADKAgent(
            adk_agent=agent,
            app_name="weather_demo",
            user_id="demo_user"
        )

        app = FastAPI()
        add_adk_fastapi_endpoint(app, adk_agent, path="/")

        if __name__ == "__main__":
            import uvicorn
            uvicorn.run(app, host="0.0.0.0", port=8000)
        ```
    </Tab>

</Tabs>
</Step>
<Step>
### Render the tool call in your frontend
At this point, your agent will be able to call the `get_weather` tool. Now
we just need to add a `useRenderToolCall` hook to render the tool call in
the UI.

<Callout type="info" title="Important">
  In order to render a tool call in the UI, the name of the action must match
  the name of the tool.
</Callout>

```tsx title="app/page.tsx"
import { useRenderToolCall } from "@copilotkit/react-core"; // [!code highlight]
// ...

const YourMainContent = () => {
  // ...
  // [!code highlight:12]
  useRenderToolCall({
    name: "get_weather",
    render: ({status, args}) => {
      return (
        <p className="text-gray-500 mt-2">
          {status !== "complete" && "Calling weather API..."}
          {status === "complete" && `Called the weather API for ${args.location}.`}
        </p>
      );
    },
  });
  // ...
}
```

</Step>
<Step>
### Give it a try!

Try asking the agent to get the weather for a location. You should see the custom UI component that we added
render the tool call and display the arguments that were passed to the tool.

<video
  src="https://cdn.copilotkit.ai/docs/copilotkit/images/coagents/tool-based-gen-ui.mp4"
  className="rounded-lg shadow-xl"
  loop
  playsInline
  controls
  autoPlay
  muted
/>
</Step>
</Steps>

## Default Tool Rendering

<DefaultToolRendering components={props.components} />

